I certainly agree, perfect copies are to be preferred but a misprinted copy is an item that should have been outsorted by the printer/publisher and scrapped. So, while not deliberately unique (as a signed copy might be), it is an oddity that is (mildly) interesting (at least to me).

Does it not seem odd that mis-printed stamps for instance are highly valuable because of their rarity but that is not true of mis-printed books ?